1. Field of the Invention
This invention concerns a method and material for sealing joints, especially joints between horizontal surfaces, such as in roadways.
2. Background Information
Roadway surfaces, either on a concrete or asphalt pavement structure or an asphalt overlay, are subjected to cracking due to thermal stresses. The cracks can be due to the stresses in the pavement structure itself, in the asphalt overlay itself, or due to stresses in the overlay due to movement of the underlying pavement structure. In any case, these cracks must be sealed in order to prevent the intrusion of water and solid debris, which will further damage the asphalt roadway. Many concrete roadway surfaces have an asphalt shoulder along side the outer edge. The joint between the concrete and the asphalt must be sealed in order to prevent the intrusion of water and solid debris.
The traditional method of sealing cracks or joints in concrete and asphalt highways has been to fill the cracks with hot applied bituminous based sealants. These work in non-moving cracks, but not in those that move, such as the reflection cracks over an expansion joint in a pavement structure. U.S. patent application Ser. No. 181,790, filed Apr. 15, 1988, assigned to the assignee of the instant application describes a self-leveling silicone composition, useful as a sealant in contact with asphalt, which cures upon exposure to moisture in the atmosphere. The composition consists essentially of a hydroxyl endblocked polydiorganosiloxane; non-acidic, non-reinforcing, treated filler; diacetamido functional silane as chain extender; aminoxysilicone compound as crosslinking agent; and non-reactive silicone fluid diluent. The cured composition has an elongation of at least 1200 percent, and a modulus at both 50 and 100 percent elongation of less than 25 pounds per square inch.
Joints in highways are being sealed by placing a backer rod in the joint space at some distance below the surface of the pavement, then placing a hot melt or cold applied sealant into the space above the backer rod up to the surface of the pavement. A similar process was attempted with the self-leveling silicone sealant described in the above referenced patent application. In cases where the vertical surfaces of the joint were not smooth and parallel, it was noted that when the self-leveling sealant was used to fill in the space over the backer rod, the backer rod did not seal tightly against the joint surfaces and the self-leveling sealant flowed down through the spaces between the side of the joint and the backer rod, resulting in "sink holes" in the sealant. In some cases, the sealant flowed through to the extent that there was no longer sufficient sealant left in place to properly seal the space between the joint sides, and a seal was not established which would prevent water and debris from getting into the joint.
A technical review of backer rods is given in the article, "Hidden, but essential", J. F. Gibbs, The Construction Specifier, March 1980, p 40. This article discusses backer rods of closed cell, flexible foam material and open cell, flexible foam. The closed cell foam backer rod has a skin on the outer surface. The open cell foam backer rod does not have an outer skin. The open cell foam can be produced by an apparatus disclosed in U.S. Pat. No. 3,869,831, issued Mar. 11, 1975. This apparatus is used to cut a sheet of foam into strands of uniform cross-sectional dimensions.
The need to establish a tight seal between the joint surfaces and the backer rod is recognized in the art. The Sealants and Waterproofers Institute Applicator Training Manual "Applying Sealants" points out that "When installing self leveling or pourable sealant, take special care installing backer rod. To prevent the sealant from leaking past the rod, all gaps or holes in the rod must be plugged. Think of it as if the joint would have to hold water, At breaks in the rod, butt the two pieces tightly together. Be sure that there are no gaps at the sides of the rod. If the backer rod is not packed tightly along the entire joint, it will float to the top of the sealant. CAUTION: Never use open cell rod with pourable sealants because of its tendency to absorb and hold moisture and possibly absorb the sealant."
The method of this invention allows a seal to be formed in an irregular joint where the joint surfaces are not smooth and parallel through the use of an open cell foam rod having an impervious skin.